There is a known technique in which, when an conductive film on a wafer is to be subjected to chemical mechanical polishing, a polishing end point of the conductive film is detected by monitoring change in a torque waveform (for example, see U.S. Pat. No. 5,069,002). The torque waveform itself measured upon polishing of the conductive film on the wafer includes various disturbances. It is important how the torque waveform is to be processed and what kind of change is to be detected in order to reliably detect the polishing end point.
Meanwhile, as another conventional technique, for example, the following end point detection method is known. In this conventional technique, a box having an arbitrary size having a vertical side h as a torque change amount and a horizontal side was a polishing time width is assumed to be present with respect to an input waveform showing the relation between polishing time and torque change. Then, the waveform is caused to input into the box at a point of h/2 in the vertical side h of one side of the box, and the torque change is analyzed according to the fact that with which side of the box the input waveform intersects with to exit to outside the box. More specifically, the inclination of the torque change is monitored by sorting the change into three types, UP when the input waveform intersects with the upper side to exit, DOWN when it intersects with the lower side to exit, and SIDE when it intersects with the other vertical side to exit. In this box method, the track of the input waveform is analyzed by adjusting the size of the box, and the point when an nth peak or valley is detected in an input waveform that repeats peaks and valleys is detected as a polishing end point (for example, see U.S. Pat. No. 5,190,614).
Furthermore, as another conventional technique, for example the following polishing end point detection device is known. In this conventional technique, a polishing device for polishing and removing an adhering material which is adhering on an undercoat material and different from the undercoat material has a measurement mechanism which measures the torque of at least either one of a first rotating shaft which drives a platen and a second rotating shaft which rotates a substance to be polished and a determination means which determines the fact that at least either one of the torque measured by the measurement mechanism and the temporal differentiation value of the torque is changed equal to or more than a set value, which is provided in advance. In the next stage of the measurement mechanism, a low pass filter having a cut-off frequency corresponding to a rotating speed lower than the rotating speed that is larger among the rotating speed of the first rotating shaft and the rotating speed of the second rotating shaft or a notch filter having a notch frequency corresponding to the rotating speed of at least either one of the rotating speed of the first rotating shaft and the rotating speed of the second rotating shaft is inserted so as to remove noise from the measured torque, and a polishing end point is detected from the determination result of the determination means (for example, see Japanese Patent Application Laid-Open (kokai) No. 1994-315850).
Meanwhile, as a conventional technique relating to the polishing end point detection method, for example, the following end point detection method is known. In this conventional technique, a box having an arbitrary size having a vertical side h as a torque change amount and a horizontal side was a polishing time width is assumed to be present with respect to an input waveform showing the relation between polishing time and torque change. Then, the waveform is caused to input into the box at a point of h/2 in the vertical side h of one side of the box, and the torque change is analyzed according to the fact that with which side of the box the input waveform intersects with to exit to outside the box. More specifically, the inclination of the torque change is monitored by sorting the change into three types, UP when the input waveform intersects with the upper side to exit, DOWN when it intersects with the lower side to exit, and SIDE when it intersects with the other vertical side to exit. This box method is good at analyzing the track of the input waveform by adjusting the size of the box. Therefore, this method is suitable for the case in which the point at which an nth peak or valley in an input waveform repeating peaks and valleys is detected is assumed as an end point (for example, see U.S. Pat. No. 5,190,614).
Moreover, as another conventional technique relating to a polishing end point detection method, for example the following polishing end point detection device is known. In this conventional technique, a polishing device for polishing and removing an adhering material which is adhering on an undercoat material and different from the undercoat material has a measurement mechanism which measures the torque of at least either one of a first rotating shaft which drives a platen and a second rotating shaft which rotates a substance to be polished and a determination means which determines the fact that at least either one of the torque measured by the measurement mechanism and the temporal differentiation value of the torque is changed equal to or more than a set value, which is provided in advance, and the polishing end point is detected according to the determination result of the determination means (for example, see Japanese Patent Application Laid-Open (kokai) No. 1994-315850).
Furthermore, as another conventional technique relating to a polishing end point detection method, for example, the following etching end point determination method is known. This conventional technique is an end point determination method of dry etching using a emission spectrography, wherein, in order to improve precision of end point determination, the sampling period of emission intensity is shortened as much as possible within the permissive range of the ability of a digital arithmetic processing device to increase the number of sampling, and the value averaged while moving at every sampling time, in other words, a moving average value is used as a new sampling value, thereby removing the noise components of actual measurement values. A primary differential value obtained from the moving average sampling values is further subjected to moving averaging, and a difference therebetween is obtained, and a moving average value of the difference value is further used to obtain a secondary differential value of the emission intensity, thereby detecting the end point of etching at high precision (for example, see Japanese Patent Application Laid-Open (kokai) No. 1986-53728).
In the conventional technique described in U.S. Pat. No. 5,069,002, the polishing end point is detected by monitoring the torque waveform measured upon polishing. However, the torque waveform itself includes various disturbances. Therefore, the polishing end point cannot be detected merely by simply monitoring the change in the torque waveform. In order to develop it to a practical level, it cannot be applied to an actual process unless any variation of the torque waveform after processing the obtained torque data can be detected somehow.
In the conventional technique described in U.S. Pat. No. 5,190,614, the point at which the nth peak or valley is detected in the waveform which shows the relation between the polishing time and torque change and repeats peaks and valleys is detected as the polishing end point. However, there is sudden reduction or the like at the polishing end point in the torque change upon polishing of the conductive film on the wafer. Therefore, when the box is applied, there is a problem that the polishing end point cannot be detected unless the condition that UPs and DOWNs are continuously detected n times is satisfied, and the polishing end point is erroneously detected when the polishing torque of an conductive film on a wafer having an individual difference. In addition, the analysis of the torque change is digitally determined by “0” and “1” wherein exit of the torque waveform to outside the box is waited for after it is input into the box. Therefore, analysis of the inclination degree (numerical value) of the waveform is not performed, parallel use of an application algorithm is difficult, and detecting the polishing end point in real time is difficult. Moreover, disturbances of drift components such as the surface state of a polishing pad cannot be removed.
In the conventional technique described in Japanese Patent Application Laid-Open (kokai) No. 1994-315850, noise is removed by using the low pass filter and the notch filter, and the polishing end point is detected by the differential value of the torque from which the noise is removed or the differential value of the torque. Hereinafter, different points between the conventional technique described in Japanese Patent Application Laid-Open (kokai) No. 1994-315850 (hereinafter, simply referred to as the conventional technique) and the present invention will be described, for example, about the removing method of the disturbances relating to the torque waveform and the way how the information relating to the polishing end point is to be determined in the state disturbance elements are removed.
In the conventional technique, the disturbances are removed by using the low pass filter and the notch filter. However, for example, low-frequency noise cannot be removed merely by the low pass filter. Therefore, in order to remove such periodic noise, periodic oscillation caused by rotation of the platen and the head is removed by the notch filter. The materials to be processed in the conventional technique are planarly formed magnetic devices, optical parts, electrical wiring, optical wiring and the like. However, in such series of parts, the noise state during polishing is expected to be constant at the beginning and after finish of the polishing, and the case in which it is changed merely in the vicinity of polishing end is expected. Therefore, among the periodic oscillation to be removed, merely fixed periodic components that is the rotation of the platen and the polishing head are removed.
On the other hand, the oscillation generated in the material to be polished in the present invention is apparently different from the vibration state in such wide polishing processing process. First of all, in a planarization process treated in the present invention, minute irregularities are present on the surface of a wafer, and a multi-layer wiring or the like is formed by planarizing the minute irregularities. Such minute irregularities are uniformly formed in the wafer surface state having swellings, and, upon polishing, the minute irregularities are required to be planarized while uniformly polishing along with such swellings. Therefore, the friction condition upon polishing is apparently different between the wafer surface state at the beginning of polishing and the wafer surface state immediately after polishing is finished. At the beginning, since there are minute irregularities, the friction force is large, and, corresponding to that, disturbances caused by unique oscillation of various members are mixed.
However, in the vicinity of polishing end, the wafer surface is comparatively smooth and the friction force is also small since sufficient planarization that ensures the focal depth of a stepper for forming multi-layer wiring is achieved. Therefore, corresponding to that, the ratio that the disturbance elements due to unique oscillation of various members are mixed is also small. As described above, in the polishing process used in device wafer planarization in the present invention, the oscillation state is apparently changed between the vicinities of the beginning and end of polishing, and the disturbance condition mixed in the torque waveform is also largely changed.
The method for removing fixed noise has been described in the conventional technique; however, such method can never be utilized for removing the disturbance components of the torque waveform in device wafer planarization, since the periodic components that continuously varies in real time is more dominant as disturbance elements in planarization CMP rather than the fixed periodic components such as the platen or polishing head. Therefore, as a disturbance removing method of the torque waveform in device wafer planarization, removing periodic noise that continuously varies in real time is required instead of fixed periodic noise.
Furthermore, in CMP that is necessary for planarization of semiconductor device wafers, the factor that varies torque is not only the state of the wafers. The surface state of a polishing pad that is changed by dressing is also a large factor of torque variation. For example, since the polishing pad surface is largely dressed (conditioned) when dressing is performed by a dresser having a large dressing effect, the friction force between the wafer and the polishing pad is increased, and, as a result, the monitored toques is also increased. On the other hand, since clogging occurs in the polishing pad when dressing is not performed, the wafer slides on the polishing pad, and the monitored torque is reduced.
In the present invention, there are a case of in situ dressing and a case of interval dressing often depending on the polishing process. In situ dressing is the case in which dressing is performed at the same time as polishing. In interval dressing, dressing is performed in the period between polishing and polishing, and dressing is not performed during polishing. Particularly, in the case of interval dressing, clogging in the surface state of the polishing pad is slightly and gradually progressed during polishing since dressing is not performed during polishing although dressing is performed before polishing. As a result, regardless of the surface state of the wafer, torque of the polishing is gradually reduced even when a normal blanket oxide film wafer is polished.
In the case of in situ dressing, the torque is constant in principle when dressing corresponding to the degree of clogging in the plane of the polishing pad is performed in real time in accordance with the clogging of the polishing pad. However, in practice, a small dresser is used, and dressing is performed by causing the dresser to scan in the radius direction of the polishing pad. Therefore, in principle, the clogging of the polishing pad cannot be removed at once, and merely part of the polishing pad is subjected to dressing in one rotation of the platen; therefore, the torque monitored as a result is not completely constant, and a torque waveform corresponding to the scan of the dresser is observed.
When torque is actual monitored in this manner, not only the torque variation due to the surface state of the wafer is always monitored, and the torque variation corresponding to the state of the polishing pad and the state of dressing during polishing is also mixed as disturbance elements. The waveform of the disturbance element due to the surface state of the polishing pad is gradually changed as a kind of drift; therefore, it cannot be removed as the periodic noise described above. Also, it is obvious that it cannot be removed even by the low pass filter. Therefore, even when the periodic waveform variation is removed, removing the noise that gradually varies along with the change in the surface state of the polishing pad is difficult, and it is expected that such disturbances are erroneously detected in the conventional method.
The conventional technique of U.S. Pat. No. 5,190,614 is suitable for the case in which the point at which an nth peak or valley is detected in an input waveform which shows the relation between polishing time and torque change and repeats peaks and valleys is determined as an end point. However, the torque variation upon polishing of the conductive film on a wafer is suddenly increased or reduced upon polishing end. Therefore, when the box is applied, there is a problem that the polishing end point cannot be detected unless the condition that UPs or DOWNs are continuously detected n times is satisfied, and there is a possibility that the polishing end point is erroneously detected when the polishing torque of the conductive film on the wafer having an individual difference is monitored.
Furthermore, in the conventional technique described in Japanese Patent Application Laid-Open (kokai) No. 1994-315850, the sampled torque value itself or the temporal differentiation value of the torque value is compared with a set value, which is provided in advance, to detect the polishing end point. However, since there are individual differences in the conductive films on wafers, when the sampled torque value itself is compared with the set value, which is provided in advance, the polishing end point may be erroneously detected as well as the above described case.
The conventional technique of Japanese Patent Application Laid-Open (kokai) No. 1986-53728 is an end point determination method upon dry etching for a silicon oxide film or the like on a semiconductor wafer. The number of sampling is increased, and the moving average value of the actual measurement value thereof is used as a sampling value; thus, the noise components in the actual measurement values are removed, and the etching end point is detected at high precision.
Thus, a technical problem to be solved is generated in order to reliably detect polishing end at high precision without erroneous detection in the wafer state at the point of polishing end by monitoring change in the torque waveform by removing continuously varying periodic noise in real time and detecting the change in the torque waveform, which is purely caused by the wafer state, while removing the noise not caused by the wafer state such as dressing conditions and drift noise caused by the state of the polishing pad and separating the noise component.